The present disclosure relates to a system for the secondary suspension of a superstructure of a rail vehicle. The system includes a steel spring as a passive spring element arranged between the superstructure and a bogie. The steel spring ensures as least one raised traveling level NF for the superstructure when the rail vehicle is traveling.
A secondary suspension between a superstructure and a railborne bogie of a rail vehicle is used particularly for the additional vibration isolation of the superstructure in order to permit a comfortable travel when conveying passengers. In many cases, the secondary suspension also interacts with a roll control for the superstructure. In addition to the secondary suspension used for the increase of comfort, a rail vehicle of the type of interest here also has a primary suspension. The primary suspension acts between the wheel axles of the rail vehicle and the bogie and is used predominantly for absorbing hard shocks to which the rail vehicle is subjected during its travel as a result of an uneven rail guidance and the like.
It is generally known to use conventional steel springs for the secondary suspension in addition to a pneumatic suspension or hydropneumatic suspension. The superstructure is normally cushioned with respect to the bogie by way of two such passive spring elements, in which case the bogie normally carries a pair of wheel axles which establish the contact with the rail.
However, when a secondary suspension is constructed by steel springs as passive spring elements, the problem arises that the superstructure level may change as a function of the loading. As used in the present disclosure, the superstructure level is the vertical level of the superstructure relative to the bogie or to the ground.
From European Patent Document EP 0 663 877 B1, a system for the secondary suspension is known which avoids the above-noted problem in that no steel springs are used for the secondary suspension. On the contrary, the secondary suspension is implemented by a hydropneumatic spring unit. The hydropneumatic spring unit consists of a spring leg and of a hydropneumatic pressure accumulator. These assemblies carry out the function of cushioning the superstructure as well as the function of damping the spring excursions. The spring leg is fastened on the superstructure and on the bogie. During a spring excursion, the piston in the spring leg displaces a defined oil volume. In the hydropneumatic pressure accumulator connected with the spring leg, this oil volume acts against a gas cushion which is separated from the oil volume by a membrane and is therefore used as a springy element. The hydraulic fluid, as the liquid column, therefore takes over the function of the power transmission. Vehicle vibrations during the travel are damped by the nozzles housed in a nozzle block. As the load of the superstructure increases, the gas volume in the hydropneumatic accumulators is compressed. Without any level control system, this would result in a lowering of the superstructure, as in the case of the above-described passive spring element. However, in order to avoid this lowering, the reduction of the gas volume has to be compensated by feeding a corresponding amount of hydraulic fluid. For this purpose, the level control system is provided which carries out this compensation as a function of the distance between the superstructure and the bogie measured by a level sensor. The controlling of level changes takes place continuously and with little time delay while the vehicle is stopped. During the travel, the mean vehicle level is also continuously monitored and compensated.
In certain application cases, it is defined that, in addition to a raised traveling level NF, the superstructure also has to take up a station platform level NB which is below it and which, in a lowered position of the superstructure matches the door steps of the rail vehicles with the height of the station platform, so that an entering and exiting becomes possible without steps. Furthermore, safety-related regulations require that, despite such a lowered station platform level NB, in the case of a system failure, the superstructure of the rail vehicle can also independently take up a so-called emergency level NN situated slightly above it. This emergency level NN situated between the lowered station platform level NB and the raised traveling level NF, despite the system failure, permits an at least slow continued traveling of the rail vehicle.
In the case of the known system for the secondary suspension with an active level control, however, an emergency level NN starting from a traveling level NF can only be adjusted if sufficient stored pressure is present in the supply reservoir and the assigned valve is operated manually. Thus, an emergency level NN cannot be ensured under all conditions.
Furthermore, the known system for the secondary suspension has a fairly high-cost construction, which applies particularly to the construction of the spring leg constructed in the manner of a lifting cylinder.
The present disclosure provides for a system for the secondary suspension by which, despite a system failure, the superstructure can take up an emergency level NN from a lowered station platform level NB under any condition.
Thus, according to the present disclosure, a secondary suspension system for a rail vehicle includes a superstructure, a bogie, and a steel spring arranged between the superstructure and the bogie. The steel spring ensures at least one raised traveling level for the superstructure when the rail vehicle is traveling. Also included is a tension cylinder. When the rail vehicle is stopped, the steel spring is compressed by the tension cylinder to adjust he superstructure to a lowered station platform level below the at least one traveling level.
The present disclosure includes the technical teaching that a steel spring as a passive spring element of a secondary suspension can be compressed, when the rail vehicle is stopped, by the tension cylinder in order to adjust to the lowered station platform level for the superstructure situated below the traveling level NF. In is such an embodiment, the passive spring element is connected in parallel to the tension cylinder.
According to the present disclosure, in the event of a system failure, the tension cylinder is automatically depressurized so that the parallel steel spring rebounds. During a stoppage, that is, in the area of the station stop, this has the effect that, from the lowered station platform level NB, the superstructure arrives at a higher level, which here corresponds to the traveling level NF, so that a continued traveling of the rail vehicle becomes possible. Also, according to the present disclosure, simple construction elements are employed, such as a conventional steel spring as well as a hydraulic cylinder available as a standardized component.
The tension cylinder should preferably be arranged locally next to the steel spring while acting between the superstructure and the bogie. This arrangement ensures a good access to the tension cylinder as well as to the steel spring from the outside for servicing or repair. As an alternative, it is also conceivable to arrange the tension cylinder inside the steel spring, constructed as a coil spring, and acting between the superstructure and the bogie. In comparison to the former arrangement, this provides a space-saving housing which should be selected when required by a narrow installation situation.
Since the tension cylinder has to follow not only vertical but also transverse and longitudinal movements of the superstructure relative to the bogie, it should be equipped with a ball joint on the bogie side and the superstructure side, whereby the coupling takes place. The ball joint can be constructed either as a conventional ball joint or, in a space-saving manner, as a ball socket, in which case the pivot can be selected as a function of the diameter of the ball socket.
According to the present disclosure, a level sensor is provided for measuring the distance between the superstructure and the bogie, which level sensor, as an actual-value generator, is a component of an active level control for adjusting a desired superstructure level. Thus, the traveling level NF, as well as station platform level NB can be precisely adjusted by an electronic defining of desired values. A linear distance sensor is, for example, suitable for use as the level sensor. A space-saving arrangement is obtained when the level sensor is integrated directly in the tension cylinder.
As an alternative to this level control, it is also conceivable to achieve a level adjustment of the tension cylinder in that the latter can be moved against a final stop in order to reach the lowered station platform level NB. However, care should be taken that the hydraulic system of the secondary suspension is dimensioned such that a stored pressure exists which is sufficient for a complete lowering of the superstructure by the tension cylinder.
A hydraulic unit can be used for admitting pressure to the tension cylinder. The working line of the hydraulic unit leading to the tension cylinder can alternatively be acted upon either by a filling valve connected with a pressure source or can be relieved by a relief valve connected with a tank. The filling valve and the relief valve, being components of a level control, can be alternately controllable by an electronic control unit. In the case of an active level control, the filling valve or valves and the relief valve form actuators of a control circuit.
In order to prevent a taking-in of hydraulic oil from the tank during a deflection of the steel spring as a result of vibrating movements during the travel, the tension cylinder has a piston which takes along a piston rod originating therefrom only in the moving-in direction, whereas, in the moving-out direction, the piston is uncoupled therefrom. By this simple mechanical uncoupling, a disturbing suction intake is avoided.
As an alternative, it is also conceivable to connect a hydraulic accumulator to the working line leading to the tension cylinder. This hydraulic accumulator inserted to this extent into the level circuit permits a regulating of the level also during the travel. During a rebounding, the hydraulic accumulator will then receive hydraulic oil displaced from the tension cylinder. The filling valve and the relief valve of the hydraulic unit can remain closed during the travel. The above-mentioned hydraulic accumulator may be-constructed in the manner of a membrane accumulator.
Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings.